Process for producing low carbon silicomanganese

ABSTRACT

Low carbon silicomanganese produced by introducing into a slag free, submerged arc electric furnace charge materials comprising a mixture of gravel, ferromanganese fines, low alloy steel, coal, coke and wood chips in proportions to obtain an alloy composition of about 50 to 65 percent manganese, 20 to 31 percent silicon, 0.05 to 0.80 percent carbon, 0.10 to 0.20 percent phosphorus, a maximum of about 0.05 percent sulfur and the balance essentially iron. An electric current is passed through the submerged electrodes of the furnace to obtain carbonaceous reduction of the charged materials and molten metal is removed periodically adjacent the bottom of the furnace.

United States P'atent 191' Bliss et al.

[111 3,768,997 [451 Oct. 30, 1973 PROCESS FOR PRODUCING LOW CARBONSILICOMANGANESE [75] Inventors: Norman G. Bliss; Robert T. Wright,

both of Kingston, Tenn. [73] Assignee: The Mead Corporation, Dayton,

Ohio

[22] Filed: May 22, 1972 [21] Appl. No.: 255,777

[52] US. Cl. 75/10 R, 75/129 [51] Int. Cl. C22d 7/06 [58] Fleld ofSearch ..75/10-13, 129, 130, 133.5

[56] References Cited UNITED STATES PATENTS 3,704,114 11/1972 Wilson75/10 R 3,431,103 3/1969 Querengasser 75/11 3,149,962 9/1964 Mennenoh75/11 2,010,230 8/1935 Gustafsson..... 75/11 3,666,438 5/1972 Madronic75/11 7/1967 1 Deadrick 75/133.5 7/1968 Robiette 75/133.5

[57] ABSTRACT Low carbon silicomanganese produced by introducing into aslag free, submerged arc electric furnace charge materialscomprising amixture of gravel, ferromanganese fines, low alloy steel, coal, coke andwood chips in proportions to obtain an alloy composition of about 50 to65 percent manganese, 20 to 31 percent silicon, 0.05 to 0.80 percentcarbon, 0.10 to 0.20 percent phosphorus, a maximum of about 0.05 percentsulfur and the balance essentially iron. An electric current is passedthrough the submerged electrodes of the furnace to obtain carbonaceousreduction of the charged materials and molten metal is removedperiodically adjacent the bottom of the furnace.

12 Claims, No Drawings PROCESS FOR PRODUCING LOW CARBON SILICOMANGANESEBACKGROUND OF THE INVENTION This invention relates to a process forproducing low carbon silicomanganese and more particularly to a provcess which provides a more economical utilization of ferromanganesefines by producing low carbon silicomanganese adapted for use incontrolling carbon in the manufacture of medium carbon ferromanganese,and for use as a low carbon deoxidizing agent for the production ofsteel.

As is well known in the art to which our invention relates, the disposalof fines produced in the production of ferromanganese is a verydifficult problem. Heretofore, it has been the usual practice to remeltthe fines. This not only consumes considerable time and energy, but alsoresults in the formation of additional fines.

BRIEF SUMMARY OF THE INVENTION nace while submerged in the chargematerials to bring about carbonaceous reduction of the chargedmaterials. The molten metal alloy is removed periodically adjacent thebottom of the furnace.

DETAILED DESCRIPTION In carrying out our process for producing lowcarbon silicomanganese, we introduce into a slag free, submerged arcelectric furnace charge materials comprising a mixture of gravel,ferromanganese fines, low alloy steel, coal, coke and wood chips. Thefurnace'is thoroughly cleaned whereby all slag is removed therefromprior to introducing the charge materials. No slag should be left in thefurnace due to the fact that a slagless operation is desired so as toeliminate subsequent separation of slag from the product.

The ferromanganese fines employed in our process contain about 65 to 82percent manganese, 1.0 to 7.5 percent carbon, 0.05 to 3.00 percentsilicon, 6 to 14 percent iron and 0.15 to 0.35 percent phosphorus. Theferromanganese fines are sized from 2 inches down.

The gravel employed in our charge materials contains about 95 to 99.5percent silicon dioxide. The low alloy steel employed contains about 90to 99.5 percent iron, 0.1 to 2.0 percent manganese and less than 0.05percent phosphorus. The coal employed in the charge materials containsabout 65 to 80 percent dry fixed car bon while the coke employedcontains about 75 to 95 percent dry fixed carbon. The wood chipsemployed in our charge materials contains about 3 to 20 percent naturalfixed carbon and are employed to provide burden porosity and to controlelectrical resistivity of the furnace. The addition of wood chipsincreases resistivity. Preferably, the low alloy steel is in the form ofsteel turnings, which, in addition to iron, contain about 0.1 to 2.0percent manganese and less than 0.05 percent phosphorus. The raio ofmanganese to iron in the charge materials is maintained at 2.6 to 1 orgreater.

The charge materials are introduced into the slag free, submergedarc'electric furnace initially to fill substantially one half of thefurnace, with the electrodes buried in the charge materials current ispassed through the electrodes as the remainder of the furnace'is filledwith the charge materials. Thereafter, the charged niaterials areintroduced continuously as the materials move downwardly to thusmaintain the furnace substantially full at all times. The first removalof the molten metal alloy takes place approximately. three hours afterthe current is first passed through the electrodes.

The molten metal alloy is then removed every 2 hours. i In actualpractice, we have carried out our improved process in a 25 foot shelldiameter, 12,000 KVA, three phase submerged arc electric furnace havingthree electrodes 35 inches in diameter and a crucible approximately 18feet in diameter and 7 1/2 feet deep. The electrical load employed onthis furnace ranges from approximately 9,000 to 1 1,000 killowatts at120 to 200 volts. Since approximately 21 megawatt-hours of energy isconsumed in this furnace in two hours, the molten metal alloy is removedfrom the furnace at the end of each interval in which approximately 21megawatthours of energy have been consumed by the furnace.

To produce our low carbon silicomanganese, the charge materials areproportioned to obtain an alloy composition of about 50 to 65 percentmanganese, 20 to 31 percent silicon, 0.05 to 0.80 percent carbon, 0.10to 0.20 percent phosphorus, a maximum of about 0.05 percent sulfur andthe balance essentially iron.

As an example, the following charge mixture has been found to besatisfactory in every respect to pro duce an alloy product containing52.25 percent manganese, 26.29 percent silicon, 0.20 percent carbon,0.16 percent phosphorus, 0.02 percent sulfur and the balance essentiallyiron.

EXAMPLE FURNACE CHARGE MATERIALS 500 lb. Gravel (8.33 parts) 620 lb.Standard FeMn Fines (10.33 parts) lb. Scrap Steel Tumings (1.33 parts)230 lb. Coal (1.83 parts) 60 lb. Coke (1 part) 300 1b. Wood Chips (5parts) Analysis of charge materials was as follows 1 GRAVEL Size 2 56" X'16" sio 98.46%

MgO 0.01%

CaO 0.05%

STANDARD FERROMANGANESE FINES Sized 2" X D Fe I I.l0%

Si l.l0%

LOW ALLOY STEELIN FORM OF SCRAP STEEL TURNINGS' COAL Size 2" X Volatiles18.60% Ash 6.l% Fixed Carbon 71.80% Moisture 3.5%

COKE

Size 1'' X 1%" Volatiles 3.09% Ash 12.93% Fixed Carbon 83.97%

WOOD CHIPS Volatiles 85.05% Ash 2.20% Fixed Carbon 12.75% Moisture40.40%

The electric furnace was operated as described hereinabove for a periodof 28 2/3 days. During this time 1,452.2 net tons of alloy were producedconsuming approximately 2.02 KWH per pound of alloy. 78 percent of themanganese in the charged materials was recovered in the alloy.

From the foregoing, it will be seen that we have devised an improvedprocess for producing low carbon silicomanganese. By formingsilicomanganese from standard ferromanganese fines, we not onlyeliminate the problem of disposing of such fines but at the same timeprovide an economical process for utilizing such fines in producing lowcarbon silicomanganese which is particularly adapted for carbon controlin forming other alloys.

We wish it to be understoodthat we do not desire to be limited to theprecise examples, proportions or embodiments herein disclosed forobvious modifications will occur to persons skilled in the art.

What we claim is:

l. The process for producing low carbon silicomanganese comprising thesteps of:

a. introducing into a slag free, submerged arc, electric furnace chargematerials comprising a mixture of approximately the following parts byweight: 8.33 parts gravel, 10.33 parts ferromanganese fines, 1.83 partscoal, one part coke, 5 parts wood chips and 1.33 parts low alloy steelcontaining about 90 to 95 percent iron, 0.1 to 2.0 percent manganese andless than 0.05 phosphous,

b. passing an electric current through the electrodes of said furnacewhile the electrodes are submerged in said charged materials in anamount to obtain carbonaceous reduction of said charged materials and analloy composition of about 50 to 65 percent manganese, 20 to 31. percentsilicon, .05 to .80% carbon, 0.10 to 0.20 percent phosphorus, a maximumof about .05% sulfur and the balance essentially iron, and c. removingmolten metal periodically adjacent the bottom of said furnace.

2. The process for producing low carbon silicomanganese as defined inclaim 1 'in which said gravel contains about 95 to 99.5 percent silicondioxide.

3. The process for producing low carbon silicomanganese as defined inclaim 1 in which said ferromanganese fines contains about 65 to 82percent manganese, 1.0 to 7.5 percent carbon, 0.05 to 3.00 percentsilicon, 6 to 14 percent iron and 0.10 to 0.35 percent phosphorus.

4. The process for producing low carbon silicomanganese as defined inclaim 1 in which said ferromanganese fines range in size from 2 inchesdown.

5. The process for producing low carbon silicomanganese as defined inclaim 1 in which said coal contains about 65 to percent dry fixedcarbon.

6. The process for producing low carbon silicomanganese as defined inclaim 1 in which said coke contains about 75 to percent dry fixedcarbon.

7. The process for producing low carbon silicomanganese as defined inclaim 1 in which said wood chips contain about 3 to 20 percent naturalfixed carbon.

8. The process for producing low carbon silicomanganese as defined inclaim 1 in which said molten metal is removed at the end of eachinterval in which approximately 21 megawatt-hours of energy have beenconsumed by said furnace.

9. The process for producing low carbon silicomanganese as defined inclaim 1 in which the charge materials are initially introduced into saidfurnace to fill substantially one half of said furnace at the timecurrent is passed through said electrodes and then the remainder of saidfurnace is filled with said charge materials and said charge materialsare introduced continuously thereafter as current is passing throughsaid electrodes.

10. The process for producing low carbon silicomanganese as defined inclaim 1 in which the first removal of molten metal takes placeapproximately 3 hours after said current is first passed through saidelectrodes and then molten metal is removed every 2 hours thereafter.

11. The process for producing low carbon silicomanganese as defined inclaim 1 in which the ratio of manganese to iron in said charge materialsis at least 2.6 to 1.

12. The process for producing low carbon silicomanganese as defined inclaim 1 in which the electrical load employed on a 25 foot shelldiameter, 12,000 KVA, 3 phase submerged are electric furnace having 3electrodes 35 inches in diameter and a crucible approximately 18 feet indiameter and 7 [/2 feet deep ranges from approximately 9,000 to 11,000killowatts at to 200 volts.

=8 Il i i

2. The process for producing low carbon silicomanganese as defined in claim 1 in which said gravel contains about 95 to 99.5 percent silicon dioxide.
 3. The process for producing low carbon silicomanganese as defined in claim 1 in which said ferromanganese fines contains about 65 to 82 percent manganese, 1.0 to 7.5 percent carbon, 0.05 to 3.00 percent silicon, 6 to 14 percent iron and 0.10 to 0.35 percent phosphorus.
 4. The process for producing low carbon silicomanganese as defined in claim 1 in which said ferromanganese fines range in size from 2 inches down.
 5. The process for producing low carbon silicomanganese as defined in claim 1 in which said coal contains about 65 to 80 percent dry fixed carbon.
 6. The process for producing low carbon silicomanganese as defined in claim 1 in which said coke contains about 75 to 95 percent dry fixed carbon.
 7. The process for producing low carbon silicomanganese as defined in claim 1 in which said wood chips contain about 3 to 20 percent natural fixed carbon.
 8. The process for producing low carbon silicomanganese as defined in claim 1 in which said molten metal is removed at the end of each interval in which approximately 21 megawatt-hours of energy have been consumed by said furnace.
 9. The process for producing low carbon silicomanganese as defined in claim 1 in which the charge materials are initially introduced into said furnace to fill substantially one half of said furnace at the time current is pAssed through said electrodes and then the remainder of said furnace is filled with said charge materials and said charge materials are introduced continuously thereafter as current is passing through said electrodes.
 10. The process for producing low carbon silicomanganese as defined in claim 1 in which the first removal of molten metal takes place approximately 3 hours after said current is first passed through said electrodes and then molten metal is removed every 2 hours thereafter.
 11. The process for producing low carbon silicomanganese as defined in claim 1 in which the ratio of manganese to iron in said charge materials is at least 2.6 to
 1. 12. The process for producing low carbon silicomanganese as defined in claim 1 in which the electrical load employed on a 25 foot shell diameter, 12,000 KVA, 3 phase submerged arc electric furnace having 3 electrodes 35 inches in diameter and a crucible approximately 18 feet in diameter and 7 1/2 feet deep ranges from approximately 9,000 to 11,000 killowatts at 120 to 200 volts. 